1. Field of Invention.
The present invention relates to synthetic latex compositions and latex films produced therefrom.
2. Description of the Related Art.
Natural rubber latex is commonly used in a wide variety of applications including films made by conventional dipping, coagulant dipping with bivalent salt or acid, and heat sensitive dipping. Films made from natural rubber latex are strong, flexible and are unlikely to sag during normal use. However, natural rubber produced articles are not always preferred or desirable under all circumstances. For example, films of natural rubber may be damaged by exposure to many solvents and petroleum-based fuels. In addition, natural rubber articles may be damaged by the action of light, heat and ozone. As a result, synthetic latex is often used and desired in various goods including, for example surgical gloves, examination gloves, protective gloves such as household gloves and electrostatic discharge conductive gloves, catheters, condoms, weather balloons, toy balloons, foamed products such as mattresses and pillows, and numerous other products. The goods may be produced wholly by the synthetic latex itself or may include a layer or coating of a synthetic latex on a natural rubber base. Commonly available synthetic latexes include: nitrile rubber; polychloroprene (also referred to as neoprene); butyl rubber; fluorocarbon rubber; polyurethane; styrene-butadiene rubber (SBR); and blends of nitrile, polychloroprene, butyl rubber, fluorocarbon rubber, polyurethane, styrene-butadiene rubber.
In spite of all the synthetic latexes commercially available, most synthetic latexes do not possess all the desirable characteristics of natural rubber such as low initial modulus, high tensile strength and high elongation. In addition, films produced from synthetic latex do not typically develop as much strength early in the drying process. This high wet-gel strength is critical in a coagulated dipping process. Similarly, articles made from synthetic latex tend to be deficient in tear strength. Therefore, tears tend to be prevalent in films and result from a number of activities, including removal of an article from its form (known as "hot" tears), tears on donning, and tears during contact with sharp objects during use by the wearer.
A need therefore remains for synthetic latexes with improved compositions and viscosity control, as well as films or coatings produced therefrom having enhanced mechanical and physical properties. In particular, a need exists for films and articles having increased tear strength while minimizing the detrimental effect on modulus, elongation and tensile strength. In addition, it is desired to retain the physical properties and tear strength upon ageing of these films and articles.